1. Field of the Invention
The present invention relates to a method and a plant for manufacturing steel in an electric steel furnace.
2. Description of the Related Art
Several methods for producing steel are known in the art. Essentially two types of methods are used today, i.e., the manufacture of steel in accordance with the conventional blast furnace converter method, and the method using the electric steel furnace.
The electric steel furnace is usually charged with 80 to 100% scrap and small portions of sponge iron (reduced iron ore) from a direct reduction plant. The electric steel furnace is used as a melting vessel and the further metallurgical process takes place in a secondary metallurgical step.
It has been know since about 1980 to manufacture hot strip on the basis of thin slabs having a size of between 40-100 mm and a maximum width of 1,800 mm together with a continuous finishing train following an electric steel plant. Using this technology, at the present time about 15% of the hot strip production of about 300 million tpa is carried out. In this connection it was possible to lower the costs for producing the hot strip on the basis of an electric steel plant in conjunction with a thin slab plant by about 50% as far as the investment costs are concerned as well as the total manufacturing costs. In addition to further processing into strips and sheet metal, the process is used for producing long products, such as sections or wire.
In connection with the electric steel method, especially in the last years problems have occurred with respect to the increasing raw material prices for scrap and the low availability of scrap. In addition, components in the scrap lead to an increase of the accompanying elements copper (due to scrap copper wires) as well as of zinc and tin which, as is well known, lead to disadvantageous reductions of the quality in the material steel. Moreover, the production times required in the electric steel furnace with a sequence of tap to tap times of 50 to 70 minutes are too long in relation to the continuous casting plant.